This invention relates to a portable, infrared gas analyzer capable of measuring multiple gases in a gas sample having one or more infrared absorption gases therein for signalling the concentration of the selected gas or gases in the gas mixture, such as the exhaust gases of gasoline powered engines without resorting to the use of chopping techniques.
Infrared gas analyzers utilizing the infrared absorption principle for determining the quantity of two or more gases in a sample gas to be measured are well known in the art. The infrared absorption principle is based on the fact that the photons are absorbed by an infrared sensitive gas in proportion to the concentration of the gas. The typical prior art infrared gas analyzer relies on the use of a chopper for repeatively and continuously interrupting the infrared beam at a predetermined rate. This prior art technique is resorted to measure the "dark level" or background signal that is present when no infrared beam is applied to the analyzer. Typical prior art patent disclosing these infrared gas analyzers are disclosed in U.S. Pat. Nos. 3,932,754; 4,069,420; 4,420,687, and 4,772,790. Typically these prior art devices employ multiple thermopiles for detecting and signalling the infrared level of the infrared beam applied to the analyzer.
Most of the known prior art infrared analyzers utilized collimated or focused infrared beams in the optical portion and do not permit the infrared beam to reflect off anything but mirrors and as a result require expensive optical systems to control the infrared beams. These prior art systems require splitting the infrared beam by a physical beam splitter or a dichroic beam splitter and the like that must be properly mounted and aligned and produces optical losses due to the beam splitting designs. In addition, these devices require relatively long optical path lengths that may vary from 1-meter to more than 100-meters.